There is no official support for that in projectile (I think) but, you can use dir-local-variables and a little bit of hacking code like this:
(defun open-local-file-projectile (directory)
"Helm action function, open projectile file within DIRECTORY
specify by the keyword projectile-default-file define in
(let ((default-file (f-join directory (nth 1
(car (-tree-map (lambda (node)
(when (eq (car node) 'projectile-default-file)
(format "%s" (cdr node))))
(dir-locals-get-class-variables (dir-locals-read-from-dir directory))))))))
(if (f-exists? default-file)
(message "The file %s doesn't exist in the select project" default-file)
(add-to-list 'helm-source-projectile-projects-actions '("Open default file" . open-local-file-projectile) t)
This code search for the file defined in dir-locals-file (by default ".dir-locals.el")
and search for the key: projectile-default-file, that should be the file route, without the projectile root, then we concat the path of the project root with the default-file relative route, and check if the default-file exist, if it exist, we open it as desired.
We can trigger the "Open default file" action by pressing the tab key in the helm menu.
This code requires the libraries dash and f to work.
Feel free to ask any question about this messy code, good luck!